1. Technical Field
The present invention relates to a three-dimensional printer configured to form a raised image on a thermally expandable sheet, a three-dimensional image forming method, and a three-dimensional image.
2. Related Art
In related art, JP 64-028660 A proposes a method for forming a three-dimensional image by forming a front-back reversed image of a desired image on a rear face, on which no thermally expandable coating layer is formed, of a thermally expandable sheet with an image forming material excellent in light absorption characteristics, irradiating the image forming side of the thermally expandable sheet with light to selectively heat an image part by using the light absorption characteristics of the image forming material to expand the thermally expandable coating layer.
The coating layer formed on the front face (the face on which an image is to be printed) of the thermally expandable sheet disclosed in JP 64-028660 A has microspheres dispersed thereon, the microspheres being obtained by microencapsulating a low-boiling, vaporizable substance with a thermoplastic resin. The microcapsules expand by heat applied to the thermally expandable sheet and forms raised portions on the sheet front face.
With the technology disclosed in JP 64-028660 A, the image part is selectively heated to obtain a three-dimensional image by using the light absorption characteristics of the image forming material. If, however, the thickness of the sheet (sheet base material) before the coating layer is formed is increased, that is, if the basis weight increases, there is a problem that the heat capacity of the sheet increases and thus the quantity of heat applied to the microcapsules decreases, resulting in that the raised amount of the raised portions decreases.
The heat capacity is increased not only by the problem of the increased basis weight of the sheet base material but also when a sheet made of another material is adhered to the sheet base material. In other words, the raised amount of the raised portions resulting from thermal expansion of the coating layer varies widely depending on the magnitude of the heat capacity of the thermally expandable sheet itself.
With a thermally expandable sheet with a large heat capacity, the raised amount of the raised portions can be prevented from decreasing by increasing the quantity of heat applied thereto. A large quantity of heat applied to the thermally expandable sheet, however, causes a failure such as thermal expansion of a non-printed region.